The invention relates to an exhaust gas-detoxicating system for externally ignited internal combustion engines wherein the fuel/air mixture can be conducted, before entering the engine cylinder, through a heated-up bypass of the suction pipe for air-intake of the engine by means of a flap valve controlled as a function of an engine characteristic, which flap valve is arranged in the suction pipe and circumvented by the bypass.
In a known exhaust gas-detoxicating system of this type a flap valve directing the air/fuel mixture through the bypass is controlled in dependence on the position of the throttle valve and/or of the accelerator pedal of the engine. Thereby, the control depends on the load. However, in order to obtain a favorable exhaust gas composition, it is important, that, in the entire low speed range, a heating-up of the fuel/air-mixture takes place substantially independently of the load. Indeed, especially for low rpm's and higher load, a heating-up is desirable in order to attain favorable exhaust gas values as well as a true running of the engine.